1. Field of the Invention
The present invention is related to methods of preparing compositions enriched in compounds containing carbon chains having various degrees of saturation. The present method is related to simulated moving bed chromatography using an argentized adsorbent.
2. Background of the Invention
The use of silver ion chromatography for separation of fatty acid methyl esters (FAME) by the degree of unsaturation of the fatty acid moiety is known (Nikolova-Damyanova, B., Advances in Lipid Methodology-Five:43-123, Oily Press Library (2003)). Silver ion thin-layer chromatography (TLC) and batch column chromatography of FAME uses silver-treated silicic acid, silica gel or ion-exchange resin as a support (Nikolova-Damyanova, B., Advances in Lipid Methodology-Five:43-123, Oily Press Library (2003)). Alumina has been used without silver ion for separation of paraffins from olefins (U.S. Pat. No. 2,985,589); however, aluminosilicates were the preferred supports. Argentized (silver-ion treated) neutral alumina has also been used to separate cis from trans octadecene olefins (Chapman, L. and Kuemmel, D., Anal. Chem. 37:1598-1600 (1965)). For separation of FAME by TLC, argentized alumina has been used to separate methyl stearate, methyl oleate, and methyl linoleate (Zinkel, D. and Rowe, J., J. Chromatogr. 13:74-77 (1964)); later, these were also separated from methyl linolenate, trans configurations, and methyl esters of longer-chain fatty acids (Breuer, B. et al., J. Chromatogr. Sci. 25:302-306 (1987)). However, these analytical separations are carried out discontinuously (batchwise) and are not amenable to use in large scale to produce commercially useful quantities of composition enriched in carbon compounds having a desired degree of unsaturation.
Liquid chromatography (LC) separation of FAME on silica-based supports such as silica gel (U.S. Pat. No. 5,672,726) and silicic acid (de Vries, B., J. Amer. Oil Chem. Soc. 40:184-186 (1963)) has been reported. Argentized macroreticular ion-exchange resin, such as Amberlite XE-284 (Scholfield, C., J. Amer. Oil Chem. Soc. 57:332-334 (1980); Scholfield, C. and Mounts, T., J. Amer. Oil Chem. Soc. 54:319-321 (1977); DeJarlais, W., et al., J. Amer. Oil Chem. Soc. 60:975-978 (1983)), and argentized ion exchange resins with strong sulfonic acid groups (U.S. Pat. Nos. 4,305,882; 6,153,774; and 6,410,763) have also been used for LC separation of FAME on the basis of unsaturation and double bond isomers (cis or trans). The use of alumina as a support for separation of FAME has been advised against because it reacts with some lipids and solvents (Monchilova, S. and Nikolova-Damyanova, B., J. Sep. Sci. 26:261-270 (2004)). Silica gel is the most widely used support for LC separation of FAME (Cert, A. and Moreda, W., J. Chromatog. A 823:291-297 (1998)). However, these batch processes operate discontinuously, rendering them unattractive for large-scale separation of compounds based on desired degree of unsaturation.
It is widely taught that great care is needed in the preparation of argentized supports for the separation of lipids (Nikolova-Damyanova, B., Advances in Lipid Methodology-Five:43-123, Oily Press Library (2003); Breuer, B., et al., J. Chromatogr. Sci. 25:302-306 (1987)). Difficulties cited include the lack of robustness and homogeneity in available support materials, (Cert, A. and Moreda, W., J. Chromatog. A823:291-297 (1998)) and inherent instability due to sensitivity to light and moisture (Monchilova, S. and Nikolova-Damyanova, B., J. Sep. Sci. 26:261-270 (2004)). Recommended precautions include protecting argentized supports from exposure to light by packing into stainless steel columns (DeJarlais, W., et al., J. Amer. Oil Chem. Soc. 60: 975-978 (1983)) or wrapping with a dark cloth (de Vries, B., J. Amer. Oil Chem. Soc. 40:184-186 (1963); U.S. Pat. Nos. 6,153,774 and 6,410,763). This precaution is not limited to argentized silica; heat activation treatment of argentized alumina TLC plates was limited to 15 minutes and 70° C. to prevent darkening of the adsorbent (Breuer, B., et al., J. Chromatogr. Sci. 25:302-306 (1987)).
Although simulated moving bed (SMB) chromatography has been used for many years in the separation of sugars and petrochemicals (Juza, M., J. Chromatog. A865:35-49 (1999)), it has had limited application in separation of oily substances. SMB has been used with supercritical CO2 to extract oilseeds and separate alpha-tocopherol from oleic acid (Bertucco, A., et al., J. Supercritical Fluids 8:138-148 (1995)). A solid bed technique employing zeolites exchanged with potassium has been applied to separation of methyl oleate and methyl linoleate from methyl stearate and methyl palmitate; however, no silver ion is used in the process (U.S. Pat. No. 4,049,688).